This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Proteins must fold correctly in order to attain biological function. Concurrently, protein aggregation and misfolding are key contributors to many devastating human diseases such as Alzheimer's disease and prion-mediated infections. Unlike other more conventional molecular chaperones, the caseinolytic protease B (ClpB) and its yeast homolog heat-shock protein 104 (Hsp104) have the remarkable ability to rescue proteins from a previously aggregated state. Members of the ClpB/Hsp104 family form hexameric ring structures of ~600 kDa in molecular weight and convert chemical energy derived from ATP-binding and ? hydrolysis into mechanical work. The goal of this research is to provide a detailed mechanistic understanding how ClpB and Hsp104 facilitate the dissociation of previously aggregated proteins. We propose to use cryo-EM to study their structures.